1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly to an apparatus and a method for processing bursts.
2. Description of the Related Art
In a wireless communication system, user traffic information and communication protocol messages each include a plurality of packets, each of which has a format of a Protocol Data Unit (PDU) defined by a Medium Access Control (MAC) protocol. The PDU can be divided into a MAC header part for carrying information such as a structure, length, etc. of the PDU, and a payload part for carrying data. Each of the MAC header and the payload includes a Cyclic Redundancy Check (CRC) bit by which a receiver can detect errors.
Meanwhile, a burst refers to a bundle of one or more PDUs, and a frame refers to a bundle of one or more bursts. The receiver identifies a burst area in a frame and selectively processes only a PDU corresponding to itself.
FIG. 1 illustrates a structure of a burst including multiple PDUs in a typical wireless communication system. Referring to FIG. 1, the burst includes, for example, three PDUs. Each PDU includes a length field 110 indicating the length of the PDU, a Header Check Sequence (HCS) field 120 for error checking of a MAC header, a PDU payload field 130, and a Frame Check Sequence (FCS) field 140 for error checking of all of the PDUs. The length field 110 and the HCS field 120 belong to the MAC header part. The MAC header part may further include a header type field, a Connection Identifier (CID) field, a field in relation to encryption, etc. as well as the length field 110 and the HCS field 120.
When the receiver has received a burst as described above, the receiver recognizes the length of the first PDU 100 by referring to the length field 110 of the MAC header, and performs error checking and data processing for the corresponding PDU 100. This process can be also applied to the second and third PDUs. As described above, the receiver accumulates the length by referring to the length field 110 within the PDU MAC header, and finishes the PDU processing when the accumulated length reaches a length of one burst.
FIG. 2 is a flow chart illustrating a process in which a receiver processes bursts in a conventional wireless communication system. Referring to FIG. 2, the receiver first receives a frame from a transmitter in step 202. Then, in step 204, the receiver selects a burst corresponding to itself from among multiple bursts, and stores the selected burst. Then, in step 206, the receiver decodes a PDU MAC header. In step 208, the receiver checks if there is an error in the PDU MAC header, using the HCS field of the PDU. As a result of the checking, the receiver proceeds to step 216 when there is an error in the PDU MAC header, and proceeds to step 210 when an error is not detected in the PDU MAC header.
In step 210, the receiver normally processes the data because an error does not exist in the PDU MAC header. Then, in step 212, the receiver determines if there is another PDU other than the data-processed PDU. When there is another PDU other than the data-processed PDU, the receiver repeats the process by returning to step 204. However, when there are no more PDUs besides the data-processed PDU, the receiver proceeds to step 214. In step 214, the receiver determines if there is another burst to be processed. As a result of the determination, the receiver repeats the process by returning to step 206 when there is another burst to be processed, and ends the processing of the bursts when there are no more bursts to be processed.
Meanwhile, the determination in step 208 concludes that there is an error in the PDU MAC header, the receiver stops the processing of the entire burst including the erroneous PDU, and performs decoding of a next burst in step 216.
According to the conventional burst processing method as described above, when an error has occurred in a MAC header of a PDU, it is impossible to process the PDU any more. According to a result of measurement of the size of packets transmitted in a wireless communication system, packets having sizes smaller than 64 bytes occupy about 50% of all the packets, and packets having sizes smaller than 128 bytes occupy about 76% of all the packets. This implies that most of the transmitted packets are not large in size. According to an estimation based on such a result, a burst having a size of 1200 bytes includes about twelve PDUs. At this time, a MAC header occupies about 6% of overhead in a PDU. This implies that, when a burst has an error, it is highly probable that the MAC header part has the error. That is, due to the error in the PDU MAC header, the receiver cannot process the payload field, either. This may cause retransmission of bursts, which may degrade the efficiency in use of resources and the performance of the entire system.